JP2006011265A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus using an intermediate transfer body, with which superior transferability can always be obtained and which appropriately copes with abnormalities, when there is an abnormality on the intermediate transfer body. <P>SOLUTION: An output current detecting part 234 detects transfer bias state in a 2nd transfer part 210 for transferring an image formed on an intermediate transfer body belt 136 to printing paper over a prescribed range, corresponding to an image forming range on the intermediate transfer body belt 136. A decision part 236 and a transfer output voltage determining part 238 adjust the transfer bias as an image forming condition, by controlling a transfer high-voltage power source 222 based on the result of detection. When the decision part 236 decides that the result of detection is abnormal, an abnormality-countering processing part 260 performs disposal to cope with the occurrence of characteristic abnormality on the intermediate transfer belt 136 as storing abnormality history in a storage part 262, informing the user of the abnormality information by an informing part 264 or stopping image forming processing via a stop control part 266. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming method and an image forming apparatus for forming an image on a predetermined output medium such as a printer, a copying machine, a facsimile machine, or a multifunction machine having the functions thereof. More specifically, an image (usually referred to as a toner image) obtained by developing a latent image on an image carrier using an electrophotographic method or an electrostatic recording method is an intermediate transfer member (primary transfer material). The present invention relates to a technique for forming an image by applying a transfer electric field to an intermediate transfer member and transferring a visible image (transfer image) on an intermediate transfer member to an output medium as a secondary transfer material.

  For example, a printer device, a copying device, a facsimile device, a copying device, or a multi-function device having a plurality of these functions, and the like, after performing desired image processing on the input image, a predetermined output image corresponding to this image is output. There is an image forming apparatus that forms on a medium.

For example, in the case of an image forming apparatus that supports color output, RGB (or Lab (correctly L ^* a ^* b ^* )) image data obtained by reading a document is used as a color suitable for subtractive color mixing according to the output side. Convert to signal. For example, at least three (preferably four) from the Lab color system represented by the Lab signal, for example, the YMC color system represented by each color signal of yellow (Y), magenta (M), and cyan (C) Mapping processing to a system or a CMYK color system with black (K) added thereto generates raster data that has been color-separated for print output. This raster data is sent to a print engine that forms an image corresponding to the read original image on the printing paper. The print engine forms an image on printing paper of a predetermined size based on the received raster data.

  The configuration of the engine unit, which is a main part related to image formation of the image forming apparatus, is, for example, one that forms a color image by repeating the same image forming process for each output color of K, Y, M, and C. An image of each color is formed on an image carrier such as a photosensitive drum in order by one engine (photosensitive unit), and this is overlaid and transferred onto an intermediate transfer member (primary transfer material) one color at a time. After the toner image on the body (here functioning as an image carrier) is transferred to the printing paper as the output medium (secondary transfer material), the toner image is made a permanent fixed image on the printing paper in the process of passing through the fixing device. There is a multi-pass type (cycle type) color image forming apparatus that forms a color image by fixing.

  This multi-pass type color image forming apparatus needs to superimpose and transfer one color at a time to the intermediate transfer member when outputting a color image, and the number of output colors is four times as large as when outputting a monochrome image (four times in the previous example). The output processing time FCOT (First Copy Out Time) from when the output command is issued until the output is discharged becomes long, and the productivity is inferior.

  In order to further shorten the output processing time FCOT at the time of color image output in the multi-pass type, a plurality of engines corresponding to each output color are arranged in-line in the order of K → Y → M → C, for example, K, Tandem configured to process Y, M, and C images in parallel (simultaneously) with four engines, that is, to form an image on the intermediate transfer member one color at a time according to the arrangement position. Type color image forming apparatuses (see Patent Documents 1 and 2).

JP-A-8-65530 JP 2000-261676 A

  Any of the above methods is common in that it is of an intermediate transfer (IBT) method having an intermediate transfer mechanism.

  Here, the transfer device forms a strong electric field between the transfer material (intermediate transfer member or output medium) and the image carrier (photosensitive drum or intermediate transfer member) at the transfer site, and the toner on the photosensitive drum or intermediate transfer member. A transfer action for electrically transferring the image to the transfer material, and a toner holding charge for holding the toner on the transfer material until the transfer material is separated from the photoreceptor and fixed as a permanently fixed image in the fixing device. It has the effect of supplying electric charge to the transfer material.

  On the other hand, in recent years, color image forming apparatuses such as color printers and color copiers are required to improve the output image quality. In particular, the gradation of the density and its stability have a great influence on the judgment of the quality of an image given by a human.

  Here, when the transfer material is allowed to pass through the transfer portion and a transfer bias is applied to the transfer means together with this, the toner image on the image carrier side is transferred to the transfer material by the action of the electric field formed thereby. In order to improve image quality, it is required to always apply a stable transfer bias in order to always obtain good transferability.

  One method for this purpose is to detect the output current value of the transfer roller in order to control the amount of charge applied to the back surface of the transfer material, and to perform feedback control depending on whether or not the detected output current has reached a desired value. A mechanism for current control is applied.

  As an example of this current control, there is a mechanism having a current monitoring function for constant voltage control of an intermediate transfer member and a transfer roller (RTR; Belt Transfer Roller). For example, a bias control method (ATCV control method: Active Transfer Voltage) in which a transfer roller that estimates the current that flows when paper is passed before the transfer operation holds a required voltage (generated voltage) by applying a constant current to the transfer roller and applies it during transfer. Control).

  Alternatively, Patent Document 3 discloses an image forming apparatus to which an image forming process including a means for uniformly charging an image carrier and a transfer means for transferring a toner image formed on the image carrier surface to a transfer material in contact with a transfer material. The transfer output control means for controlling the transfer output applied to the contact transfer means is a voltage control means, the output current detection means for detecting the output current value at the time of constant voltage control by the transfer output control means, and the output current is A determination means for determining whether or not a desired value has been reached, and a means for determining a transfer output voltage to the contact transfer means from a constant voltage output value based on the determination means and an input calculation result from the output current detection means A mechanism has been proposed in which a transfer output control operation is performed at least once before a printing operation, and an output current during the printing operation is monitored and corrected.

JP-A-6-138784

  According to the mechanism described in Patent Document 3, it is possible to always allow an appropriate current to flow through the transfer material, and transfer high-pressure control, which has conventionally been configured by hardware, is performed via software. The circuit configuration is simplified, the cost can be reduced, and a more flexible sequence can be realized, so that stable transfer high-pressure control can be realized.

  For example, there is a cycle called “Setup” that is performed at a specific timing in order to realize constant voltage transfer. The output value can be determined so that an arbitrary constant voltage can be output by performing current monitoring (monitoring) on the transfer output determined at the time of setup and calculating the resistance value at that time.

  However, in the mechanism described in Patent Document 3, current monitoring is started when the bias transfer roller comes into contact with the primary charged portion, and the setup cycle is asynchronous with the belt-shaped intermediate transfer member. Only the shortest timing at which the resistance value can be calculated (current monitoring for one turn of the bias transfer roll) is performed.

  For this reason, when the mechanism described in Patent Document 3 is used in a transfer apparatus using an intermediate transfer member, it is not possible to monitor the current portion of the intermediate transfer member in the circumferential direction, and the intermediate transfer member itself can be monitored over time. Alternatively, there is a problem that it is not useful for detecting partial changes in transfer characteristics and partial unevenness due to specific factors such as partial fatigue.

  The present invention has been made in view of the above circumstances, and even in an image forming apparatus using an intermediate transfer body, good transferability can always be obtained, or appropriate when an abnormality exists in the intermediate transfer body. The purpose is to propose a mechanism that can cope with this.

  According to the first image forming method of the present invention, a latent image is formed on a first image carrier, and an image obtained by developing the latent image is transferred onto a first transfer material. By using the first transfer material as the second image carrier and transferring the image transferred on the second image carrier to the second transfer material, the second transfer material on the output medium. An image forming method for forming an image, wherein an image formed on a second image carrier is transferred when the image formed on the second image carrier is contact-transferred to a second transfer material by a transfer unit. The transfer bias state in the transfer portion is detected over a predetermined range corresponding to the above, and the image forming conditions are controlled based on the detection result.

  In the second image forming method according to the present invention, a latent image is formed on the first image carrier, and an image obtained by developing the latent image is transferred onto the first transfer material. By using the first transfer material as the second image carrier and transferring the image transferred onto the second image carrier to the second transfer material, the second transfer material on the output medium. An image forming method for forming an image on a second image carrier when the image formed on the second image carrier is transferred to the second transfer material by a transfer unit. The transfer bias state in the transfer portion is detected, and it is determined whether or not the detection result exceeds a predetermined normal range. If the detection result exceeds the predetermined normal range, a characteristic abnormality occurs in the first transfer material. It was decided to perform an abnormality handling process according to what is being done.

  A first image forming apparatus according to the present invention is an apparatus suitable for carrying out the first image forming method according to the present invention, and is provided on a second image carrier (that is, a first transfer material). A transfer portion that contacts and transfers the image formed on the second transfer material and a predetermined range corresponding to the image formation range on the second image carrier (that is, the first transfer material) in the transfer portion. And a control unit that detects a transfer bias state and controls image forming conditions based on the detection result.

  The second image forming apparatus according to the present invention is an apparatus suitable for carrying out the second image forming method according to the present invention, and forms a latent image on the first image carrier. The image obtained by developing the latent image is transferred onto a first transfer material, and the first transfer material is used as a second image carrier to be transferred onto the second image carrier. An image forming apparatus that forms an image on an output medium that is a second transfer material by transferring the transferred image to a second transfer material, and the image formed on the second image carrier is The transfer bias state in the transfer part that contacts and transfers to the second transfer material and the predetermined range of the second image carrier is detected, and it is determined whether or not the detection result exceeds a predetermined normal range. A characteristic abnormality occurs in the first transfer material on condition that the determination unit and the determination unit determine that the predetermined normal range is exceeded A process according to which was assumed and a anomaly correction unit that performs.

  This second image forming apparatus is more preferably combined with the first image forming apparatus according to the present invention.

  The inventions described in the dependent claims define further advantageous specific examples of the image forming apparatus according to the present invention.

  For example, it is desirable that the control unit includes a transfer bias control unit that controls a transfer bias in the transfer unit.

  In addition, the first transfer material is preferably composed of an endless belt. In this case, the transfer bias control unit is a predetermined belt-circulating direction of the first transfer material (that is, the second image carrier). It is preferable to control the transfer bias over a range. Preferably, the output current detector may detect the output current value at a plurality of positions in one cycle (all circumferences) of the first transfer material in the belt rotation direction.

  The transfer bias control unit includes a voltage control unit that controls a transfer output applied to the transfer unit, an output current detection unit that detects an output current value during constant voltage control by the voltage control unit, and an output current. It is preferable to have a transfer output voltage determination unit that determines a transfer output voltage to the transfer unit controlled by the voltage control unit based on the output current value detected by the detection unit.

  The transfer output voltage determination unit transfers the output to the transfer unit based on the constant voltage output value based on whether or not the current value detected by the output current detection unit has reached a desired value and the input calculation result from the output current detection unit. The voltage should be determined.

  In addition, the abnormality handling processing unit stores a history of the occurrence of the characteristic abnormality in the first transfer material, and a notification for informing the information that the characteristic abnormality has occurred in the first transfer material. Or a stop control unit for stopping the image forming process.

  According to the first image forming method and the image forming apparatus of the present invention, the image is based on the transfer bias state in the transfer portion detected over a predetermined range of the second image carrier (that is, the first transfer material). Since the forming conditions are controlled, it is possible to set appropriate image forming conditions while detecting partial changes in transfer characteristics and partial unevenness due to specific factors such as aging or partial fatigue of the intermediate transfer body itself. It becomes like this.

  Further, according to the second image forming method and the image forming apparatus of the present invention, the transfer bias state in the transfer portion detected over a predetermined range of the second image carrier (that is, the first transfer material) is normal. It is determined whether or not the range exceeds the normal range, and when the range exceeds the normal range, the first transfer material is processed according to the occurrence of the characteristic abnormality. When a partial change in transfer characteristics or partial unevenness due to a specific factor such as partial fatigue is detected, an appropriate abnormality handling process can be executed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example when the image forming apparatus according to the present invention is applied to a printer. As shown in the drawing, the standard configuration of the printer 1 (hereinafter referred to as the printer main body 100) includes a main unit 102, an intermediate transfer member belt 136 that is an endless belt that functions as a first transfer material, and a standard discharge tray (CenterTray) 154. And a manual feed tray (SMH) 180 and a first paper feed tray (TRAY1) 190 installed on the lower side of the main unit 102.

  The printer main body 100 can be connected to an external device via a connection cable (not shown) or a network. For example, the connection cable is not illustrated by a CSMA / CD (Carrier Sense Multiple Access with Collision Detection) type LAN (Local Area Network; for example, IEEE802.3) or a Gigabit (Giga Bit) based LAN (hereinafter collectively referred to as a wired LAN). Connected to an image input terminal such as a personal computer.

  The printer main body 100 is not only used as a main body part constituting the printer 1 having a page printer function, but also a copying apparatus having a copying function, a FAX apparatus having a facsimile transmission / reception function, a page printer function, and a copying function. It can also be used as a main part as a so-called multi-function machine having a plurality of functions such as a facsimile transmission / reception function.

  For example, although not shown, a copying apparatus having a copying function can be configured by providing an image reading unit (scanner unit) that reads a document. Or, connect to an image input terminal such as a FAX apparatus or a personal computer via a public switched telephone network (PSTN), an ISDN (Integrated Switched Digital Network), or other communication media including the Internet. Thus, it is possible to configure a FAX apparatus that prints out based on FAX data acquired via the communication interface.

<Basic configuration>
The printer main body 100 uses an electrophotographic image forming process to display an image represented by image forming data (for example, image data read by a scanner or print data input from a personal computer) input from an image input terminal. Then, a visible image is formed (printed), that is, copied on a recording medium such as plain paper or thermal paper. Therefore, the main unit 102 of the printer main body 100 includes a raster output scan (ROS) -based print engine for operating the printer 1 as a digital printing system.

  Inside the main unit 102, recording paper is carried into the ROS-based scanning output system 103 side, or toner cartridges (Toner Cartridge) for each color of the scanning output system 103, Y, M, C, and K are arranged. The standard conveyance comprising various roll members (rotating bodies) 108 and the like for discharging recording paper printed by the cartridge unit 105 and the ROS-based scanning output system 103 to the standard discharge tray 154 and the manual feed tray 180. A system 107 is housed.

  The manual feed tray 180 is provided with various rolls and various paper sensors (manual feed tray paper remaining level sensor 182a, manual feed tray paper presence / absence detection sensor 182b, and manual feed tray level sensor 182c).

  As the roll member 108, for example, a manual feed tray primary feed roll 108a, a manual feed roll pair 108b, a manual take-up roll pair 108c, a resist roll pair (Regi Roll) 108d, a paper take-out roll pair 108e, and the like are provided.

  Although not shown, a tray cabinet, which is an example of a peripheral device that is optionally used in combination with the printer main body 100, can be provided below the standard discharge tray 154.

  A first paper feed tray 190 disposed below the main unit 102 includes various rolls 192 (a pickup roll 192a and a feed roll pair 192b) and various paper sensors 194 (a paper remaining level sensor 194a and a paper presence / absence detection). A feeder unit 196 comprising a sensor 194b) and a paper cassette 198 having a tray table 199 for storing recording papers of a predetermined size (which can also correspond to a plurality of sizes by changing the position of the stopper). It is configured.

  The feeder unit 196 rolls out recording sheets one by one from the sheet cassette 198 and sends them to the standard transport system 107 in the main unit 102.

  The ROS-based scanning output system 103 is an example of a first image carrier, and a drum and photosensitive bias member and a primary bias transfer roll are used to transfer an image onto an intermediate transfer belt that is an example of a first transfer material. Using this intermediate transfer belt as a second image carrier, a transfer image portion of the intermediate transfer belt and a recording paper as an example of an output medium as a second transfer material are paired with a secondary bias transfer roll pair. The image is printed (formed) on a recording medium by transferring the image onto a recording sheet by being sandwiched between the two.

  That is, the scanning output system 103 first prints the Y, M, C, and K color print execution units 130 that are juxtaposed sequentially at a certain interval in one direction (Y, M, C, and K are attached to each; other members) The same applies to the above; when referring to them together, the colors are omitted).

  The intermediate transfer belt 136 rotates in the belt conveyance direction indicated by X in the drawing, and its overall length (peripheral length) is 949.4 mm, and the interval between the print execution units 130 is 90.48 mm. Is set.

  The print execution unit 130 transfers the toner image formed on the photosensitive drum 131, which is the first image carrier, to the intermediate transfer belt 136, which is the first transfer material and is the second image carrier. It functions as a first transfer section.

  A photosensitive drum 131 is disposed at the center of the printing execution unit 130. Around the photosensitive drum 131, a cleaner 132 that collects toner remaining without being transferred onto the photosensitive drum 131, and a photosensitive drum. A primary charger 133 that uniformly charges the surface of the photosensitive drum 131 to the same polarity as the toner; a developer 134 that visualizes the latent image formed on the photosensitive drum 131 as a toner image; and a toner output signal. And a writing scanning optical system (ROS Unit) 179 including a polygon mirror 176 and other mirrors 177a, 177b, 177c, etc. Yes.

  Further, a primary bias transfer roll (BTR) 135 is disposed at the upper portion of the print execution unit 130 for each color so as to face the photosensitive drum 131 so as to sandwich the intermediate transfer belt 136. ing.

  The primary bias transfer roll 135 is, for example, an aluminum cored bar provided with a dielectric surface layer made of a predetermined resin, and is pressed against the photosensitive drum 131. As dielectric layers, in addition to fluorine resins such as PVDF, PTFE, PFA, FEP, ETFE, PCTFE, and PVF, PMMA (polymethyl methacrylate), PP (polypropylene), PET (polyethyl terephthalate), SI (silicone resin), PBT (polybutylene terephthalate), POM (polyacetal), PC (polycarbonate), PPE (polyphenyl ether), PAR (polyarylate), PAR (polyarylate), PES (polyethersulfone), PSU (polysulfone), PPS ( Resins such as polyphenylene sulfide), PA (polyamide), PI (polyimide), PAI (polyamideimide), PEI (polyetherimide), and PEEK (polyetheretherketone) can also be employed. In particular, when PVDF is employed, the dielectric strength, dielectric constant, surface properties, etc. are excellent.

  When the primary bias transfer roll 135 is supplied with electric charges from a charge supply source (not shown), the surface potential of the primary bias transfer roll 135 is charged to a predetermined bias potential (for example, about +1 kV). Yes.

  As the structure of this charging unit, for example, a low resistance rubber layer such as carbon dispersion EPDM is provided on the outer periphery of a metal core to which a voltage on which an alternating voltage is superimposed by an external power source is applied, and carbon is used as a resistance control layer on the surface. A charging roller provided with a dispersed urethane layer or epichlorohydrin rubber layer can be used. Alternatively, a charging member such as a corona charger, a blade, or a brush can be used. In order to suppress the generation of ozone and achieve high durability, it is preferable to employ a roller charging method as in this embodiment.

  The intermediate transfer body belt 136 is laid on a plurality of belt conveyance rolls 137. For example, in the figure, idle roll (Idle Roll) 137a, drive steering roll (Drive & Steering Roll) 137b, backup roll (Back Up Roll) 137c, pre-roll (Pre Roll) 137d, and tension roll (Tension Roll) 137e. One is provided.

  A secondary bias transfer roll (2nd BTR) 138 is disposed at a position facing the backup roll 137c among the plurality of belt transport rolls 137. In the vicinity of the belt conveyance roll 137b arranged on the right side in the drawing, a belt cleaning unit 140 that collects toner remaining without being transferred onto the intermediate transfer belt 136 is arranged.

  Similar to the primary bias transfer roll 135, the secondary bias transfer roll 138 is, for example, an aluminum cored bar provided with a dielectric surface layer made of a predetermined resin, and is pressed against the photosensitive drum 131. As the dielectric layer, the same material as the primary bias transfer roll 135 can be used.

  The backup roll 137c and the secondary bias transfer roll 138 are brought into pressure contact with each other, and the toner image formed on the intermediate transfer belt 136, which is the first transfer material and the second image carrier, is transferred to the second transfer material. And a second transfer unit configured to contact and transfer to a printing paper as an output medium. When the toner image arrives at the second transfer portion as the intermediate transfer belt 136 rotates, the printing paper as the second transfer material is supplied from the standard conveying system 107 to the second transfer unit in synchronization with this, and is simultaneously illustrated. The transfer bias is applied to the secondary bias transfer roll 138 by a charge supply source (for example, a transfer high-voltage power supply), and the toner image on the intermediate transfer belt 136 side is transferred to the second transfer material (output medium / printing paper). Is done.

  Therefore, for example, similarly to the primary bias transfer roll 135, the secondary bias transfer roll 138 is supplied with charges from a charge supply source (not shown), so that the surface potential of the secondary bias transfer roll 138 has a predetermined bias. It is charged to a potential (for example, about +1 kV).

  Although details will be described later, as a characteristic part of this embodiment, a voltage control unit that controls a transfer output applied to the second transfer unit is provided, and the belt rotation direction of the intermediate transfer member belt 136 configured by an endless belt is provided. The output current value at the time of constant voltage control by the voltage control unit is detected over a predetermined range, and the transfer output voltage to the second transfer unit controlled by the voltage control unit is determined based on the detected output current value. Thus, the transfer bias in the second transfer portion is controlled. As the configuration of the charging unit, the same one as the primary bias transfer roll 135 can be used.

  The secondary bias transfer roll 138 can also have a structure in which, for example, a conductive EPDM foam layer is provided on a metal core, and a dielectric layer of PVDF resin is provided on the surface thereof. As a result, a wide transfer nip is ensured at the transfer site, so that a conveying force can be provided, and the heat resistance of the backup roll 137c, the secondary bias transfer roll 138, and the like can be increased due to the influence of heat generated in the next fixing process. You can miss the low ones.

  The secondary bias transfer roll 138 may be one in which a dielectric layer of silicone rubber is provided on the surface of the cored bar. The silicone rubber layer is rich in elasticity, and can be elastically deformed to form a nip if it is applied to the backup roll 137c with an appropriate pressure. When the secondary bias transfer roll 138 forms a nip, the thickness of the silicone rubber layer (dielectric layer), which is a dielectric layer, changes, so that the electric capacity of the secondary bias transfer roll 138 changes, and at the nip portion. Since the surface potential of the secondary bias transfer roll 138 vibrates, the toner image can be efficiently transferred to the printing paper.

  The secondary bias transfer roll 138 can also employ a configuration in which a voltage is applied to the core metal from the outside. As an example, a DC voltage of about +1 kV is applied. In this case, a voltage obtained by superimposing an alternating voltage of Vpp (for example, about 2 kV) on a DC voltage (for example, about +2 kV) is applied to a charging roller metal core (not shown) by an external power source. Thereby, the dielectric breakdown of the dielectric layer of the secondary bias transfer roll 138 can be prevented and the transfer electric field can be strengthened, and the printing paper (output medium) as the second transfer material is good for a wide variety of types. Transfer performance can be realized.

  As another example, an AC voltage (for example, about Vpp 2 kV) may be applied to the core of the secondary bias transfer roll 138 from the outside. In this case, a DC voltage (for example, about +1 kV) is applied to a charging roller core (not shown). As a result, the AC voltage applied to the transfer roller mandrel can realize the charging uniformity of the transfer roller dielectric layer and, in addition, form a vibration transfer electric field at the transfer site, thereby efficiently secondizing the toner image. The transfer material can be transferred to a printing paper as a transfer material, and good transfer performance can be realized for a wide variety of second transfer materials (output medium, printing paper).

  Further, on the left side of the main unit 102 in the drawing, the recording paper transported downstream of the secondary bias transfer roll 138 in order to discharge the printed recording paper fed from the secondary bias transfer roll 138 to the outside of the apparatus. In addition, various conveying rolls such as a fixing roll (Fuser Roll) 139a and a fixing discharge roll (Fuser Exit Roll) 139b are provided. The fixing unit 139 is configured by the fixing roll 139a and the fixing discharge roll 139b.

  Further, on the downstream side of the fixing unit 139 of the standard discharge tray 154, a discharge roll 152 for discharging recording paper sent from the main unit 102 to the outside of the apparatus is provided.

  A patch (MOB; Mark On Belt) / Auto Density Control sensor 182 (hereinafter referred to as MOB & ADC sensor 182) prints with the tension roll 137e along the circumference of the intermediate transfer belt 136 of the printer main body 100. , A home position sensor 184 is provided between the print execution units 130Y and 130M, and an edge sensor 186 is provided between the print execution units 130M and 130C. .

  The MOB & ADC sensor 182 detects an unfixed toner image which is a reference image (toner patch / Mark On Belt) of an arbitrary density formed on the intermediate transfer belt 136 in order to obtain a stable image, and the detection result is Based on this, the density control is performed by feeding back the process conditions such as the exposure amount and the development bias, so that a constant gradation-density characteristic can be obtained even if fluctuations occur in each part of the apparatus. ing.

  The home position sensor 184 is provided to detect the reference position (home position) of the circumference of the intermediate transfer belt 136 and to maintain the rotational speed and phase of the intermediate transfer belt 136 at predetermined values based on the detection result. It has been.

  The edge sensor 186 is provided for detecting a side edge (edge) of the intermediate transfer belt 136 and controlling the lateral movement (steering) of the intermediate transfer belt 136 based on the detection result.

<Operation of basic configuration>
In the scanning output system 103 having such a configuration, first, the surface of the photosensitive drum 131 is negatively charged with the same polarity as that of the toner by the primary charger 133 and becomes a VD potential. Thereafter, a yellow (Y) laser light source (not shown) as an exposure light source is driven by a yellow toner output signal (for example, an on / off binarization signal), thereby converting the yellow toner output signal into an optical signal. The converted laser beam is irradiated toward the photosensitive drum 131Y. Thus, the laser beam scans the photosensitive drum 131Y charged by the primary charger 133Y after being cleaned by the cleaner 132Y, thereby forming an electrostatic latent image on the photosensitive drum 131Y. That is, the exposed portion on the photosensitive drum 131 that has undergone image exposure has a small absolute value of potential, and becomes a VL potential, thereby forming an electrostatic latent image.

  This electrostatic latent image is visualized as a toner image by the developing device 134Y to which yellow toner is supplied. That is, a thin layer of toner is coated on a sleeve (not shown) that is rotatably attached to the developing device 134, and this toner is negatively charged. Since the potential between the dark potential VD and the light potential VL of the photosensitive drum 131 is given to the sleeve by an external power source, the toner on the sleeve is transferred only to the portion of the light potential VL of the photosensitive drum 131 to be electrostatic. The latent image is visualized.

  Thereafter, the photosensitive drum 131Y and a primary bias transfer roll (BTR) 135Y are paired to convey the intermediate transfer belt 136, and the toner image is transferred to the intermediate transfer belt 136. The That is, in the process of nipping and conveying the intermediate transfer belt 136, the intermediate transfer belt 136 has a charge (main charge) of a polarity opposite to the charge (negative charge in this example) of the photosensitive drum 131 from the primary bias transfer roll 135. In the example, a positive charge) is applied, and the toner image on the photosensitive drum 131 is transferred and transferred to the intermediate transfer belt 136, which is the first transfer material, by electric attraction, so that the intermediate transfer belt 136 is transferred to the first transfer material. 2 functions as an image carrier. After the transfer, excess toner is removed (cleaned) from the photosensitive drum 131Y by the cleaner 132.

  Similarly, the photoreceptors charged by the primary chargers 133M, 133C, and 133K based on the corresponding M, C, and K toner output signals sequentially obtained at a predetermined interval with respect to the yellow toner output signal. By scanning the drums 131M, 131C, and 131K, electrostatic latent images are sequentially formed on the photosensitive drums 131M, 131C, and 131K.

  Each electrostatic latent image is sequentially converted into a toner image by developing units 134M, 134C, and 134K to which each color toner is supplied, and each toner image is placed on an intermediate transfer belt 136 by primary bias transfer rolls 135M, 135C, and 135K. Are sequentially transferred. After the transfer, excess toner is removed from the photosensitive drums 131M, 131C, and 131K by the cleaner 132.

  After this transfer, the portion of the intermediate transfer belt 136 to which the image has been transferred (transfer image portion) is conveyed in the direction of the secondary bias transfer roll 138. On the other hand, the standard transport system 107 transports the recording paper toward the contact portion between the belt transport roll 137c and the secondary bias transfer roll 138 by the resist roll pair 108d. Then, the transfer image portion on the intermediate transfer belt 136 and the recording sheet are conveyed to the downstream side while being sandwiched between the secondary bias transfer rolls 138, thereby printing the image on the recording sheet.

  The recording paper on which the toner images of each color of Y, M, C, and K are sequentially multiplex-transferred in this way is peeled from the intermediate transfer belt 136 and conveyed to a fixing unit 139 having a fixing roll 139a. The toner image is fixed by heat onto the recording paper by the heat fixing of the toner image by 139a, and then discharged to the outside such as the standard discharge tray 154.

<Configuration Example Focusing on Image Forming Process>
FIG. 2 is a functional block diagram of a configuration example focusing on image forming processing in the second transfer unit of the printer 1 (printer body 100) shown in FIG.

  The printer main body 100 includes a backup roll 137c and a secondary bias transfer roll 138, and a second transfer unit that contacts and transfers a toner image formed on the intermediate transfer body belt 136 to a printing sheet as a second transfer material. 210 and a print control unit 220 that controls the image forming conditions by detecting the transfer bias state in the second transfer unit 210 over a predetermined range in the belt circumferential direction of the intermediate transfer belt 136 configured as an endless belt. ing.

  The printing operation mechanism unit 340 includes a paper feed unit 342 including a manual feed tray 180 and a paper cassette 198, a printing unit 350 that executes a printing process, and a paper discharge process and punching hole formation for the processed paper. A discharge processing unit 360 that performs terminal processing such as processing and stapler processing. The control output signal CN0 of the print control unit 220 is connected to the paper feeding unit 342, the printing unit 350, and the discharge processing unit 360 of the printing operation mechanism unit 340.

  The printing unit 350 includes a conveyance unit 352 having a standard conveyance system 107 that conveys printing paper, a developing unit 354 having a developing unit 134 that develops characters and images formed as latent images on the photosensitive drum 131, and development. A transfer unit 356 as a print execution unit including a primary bias transfer roll 135 and a secondary transfer roll 138 that transfer characters and images made visible by the unit 354 to the intermediate transfer belt 136 and printing paper; And a fixing unit 358 (corresponding to the fixing unit 139 in FIG. 1) having a fixing roll 139a for fixing characters and images transferred onto the printing paper by the unit 356.

  In the drawing, the second transfer unit 210 including the backup roll 137c and the secondary bias transfer roll 138 is particularly extracted from the transfer unit 356.

  The print control unit 220 includes a transfer high voltage power source 222 that applies a high voltage to the secondary bias transfer roll 138, and a transfer bias control unit 230 that controls a transfer bias in the second transfer unit 210.

  As a transfer voltage control method, the transfer bias control unit 230 basically applies a constant current value to the secondary bias transfer roll 138 in a state where there is no transfer material in the transfer nip portion, and applies it from the generated voltage at the time of transfer. A method for determining the transfer voltage is adopted. Thus, by detecting the impedance (resistance value) of the entire transfer system when paper is not passed, even if the resistance value of the transfer roller changes, an appropriate transfer bias can be applied accordingly.

  For this reason, the transfer bias control unit 230 controls a transfer control applied to the transfer high voltage power supply 222 of the second transfer unit 210 and a transfer high voltage power supply 222 during constant voltage control by the voltage control unit 232. The output current detection unit 234 detects the output current value of the output current.

  Further, the transfer bias control unit 230 determines whether the output current detected by the output current detection unit 234 has reached a desired value, and based on the output current value detected by the output current detection unit 234. A transfer output voltage determination unit 238 that determines a transfer output voltage to the second transfer unit 210 (specifically, the transfer high-voltage power supply 222) controlled by the voltage control unit 232.

  The voltage control unit 232 has a function of digitally increasing or decreasing the voltage applied to the secondary bias transfer roll 138 by controlling the transfer high voltage power supply 222.

  The output current detection unit 234 has a function of detecting current flowing from the secondary bias transfer roll 138 into the backup roll 137c. The timing for detecting the current is the same as when the paper is not passed as in the ATCV system. In order to correct the circumferential unevenness of the intermediate transfer member belt 136, the voltage generated for one turn of the intermediate transfer member belt 136 (the resulting current monitor) Value) is sampled and averaged as the current monitor range.

  The range that requires current monitoring is not limited to one round, but may be a range corresponding to the image forming range (corresponding to the output size in the circumferential direction). When a certain range in the belt 136 is set as the transfer range, only the transfer range (corresponding to the output size in the circumferential direction) may be set as the current monitor range.

  As this non-sheet-passing, for example, the front multi-rotation immediately after the power is turned on, cleaning of the surface of the photosensitive drum 131 and the intermediate transfer belt 136 performed at the time of starting up the laser printer, uniformizing the surface potential, and It is preferable to use a set-up time that is performed immediately before the printing operation or a series of device driving for the purpose of heating the fixing unit 139 or the like. By doing so, it is not necessary to provide a dedicated processing cycle for current monitoring, and the output processing time FCOT (First Copy Out Time) from when the output command is issued until the output is discharged is not affected.

  The transfer output voltage determination unit 238 uses the determination result of the determination unit 236 to determine whether or not the inflowing current has reached a desired value, so that the current flowing from the secondary bias transfer roll 138 to the backup roll 137c is constant. The value is converged to enable control equivalent to that of the ATCV type constant current circuit.

  That is, the transfer output voltage determination unit 238 receives the constant voltage output value based on the determination result CN3 of the determination unit 236 and the input calculation result from the output current detection unit 234 detected over a predetermined range in the circumferential direction of the intermediate transfer belt 136. The transfer output voltage to the second transfer unit 210 is determined based on the above. From the relationship between the current and voltage, the result is equivalent to detecting the resistance value of the second transfer unit 210 before the printing operation.

  For example, the transfer output voltage determination unit 238 refers to the determination result of the determination unit 236 and supplies control information CN1 for changing the voltage digitally to the voltage control unit 232. When the control information CN1 from the transfer output voltage determination unit 238 is input to the voltage control unit 232 in this way, the voltage control unit 232 starts an operation of digitally changing the voltage with respect to the transfer high voltage power source 222. As an example, the voltage control unit 232 converts the voltage to an analog voltage of 0 to 5 V, and further controls the output voltage of the transfer high voltage power supply 222 within a range of 0 to 5 kV.

  That is, the transfer bias controller 230 converges the current flowing from the secondary bias transfer roll 138 to the backup roll 137c to a constant value by monitoring the output current over a predetermined range in the circumferential direction of the intermediate transfer belt 136. Thus, a PTVC (Programmable Transfer Voltage Control) system for controlling the transfer bias of the second transfer unit 210 is adopted.

  Note that the current flowing through the transfer material is detected while the printing paper as the second image carrier passes through the second transfer unit 210 constituted by the backup roll 137c and the secondary bias transfer roll 138. By correcting the transfer output voltage, more accurate control can be performed. In this case, the transfer current latitude is widened by providing a certain range rather than reducing the value of the transfer current to a constant value. Limiting to a constant value has the same effect as performing constant current control. As a result, during small-size paper transfer, a large amount of transfer current flows at the portion where the secondary bias transfer roll 138 and the backup roll 137c are in contact with each other. This is to avoid a problem that becomes defective.

  The transfer current is affected by environmental fluctuations and varies depending on the resistance of the secondary bias transfer roll 138 that is the first transfer material (and the second image carrier) and the resistance of the printing paper that is the second transfer material. However, by performing current monitoring while feeding paper and applying feedback control to the transfer voltage, the control accuracy of the transfer bias is improved and printing can be performed in a stable state. As a result, it is possible to prevent image failure due to transfer failure, occurrence of plus memory, transfer failure of small size paper, excessive transfer current in a high humidity environment, and the like, and good transfer performance can be realized.

  When a transfer material whose resistance value is significantly different from the expected transfer material resistance value is used, such as when the resistance value of the transfer material is high or low, the transfer current that you want to flow during printing is the appropriate transfer current value. May deviate from range. When the impedance of the transfer material changes greatly, the transfer current becomes excessive or insufficient, and an image defect occurs. In particular, as the type of the second transfer material used for printing increases, the resistance of the second transfer material also diversifies and it is difficult to obtain a good image regardless of the environment and the type of transfer material. Become.

  On the other hand, when the second transfer material passes through the pressure nip portion between the secondary bias transfer roll 138 and the backup roll 137c of the second transfer unit 210, the second transfer material is constant after the second transfer material is inserted. If the output voltage of the transfer high-voltage power supply 222 is corrected according to the current detection result of the output current detection unit 234 after the time, the voltage correction value is used as the resistance detection result of the second transfer unit 210 before the printing operation. By changing according to the current detection result, it becomes possible to obtain a good image regardless of the resistance value of the second transfer material, that is, the second transfer material having any resistance value.

  The determination unit 236 included in the transfer bias control unit 230 determines whether the difference between the output current values at a plurality of positions on the intermediate transfer belt 136 detected by the output current detection unit 234 exceeds a predetermined normal range. To do.

  Further, the print control unit 220 responds that a characteristic abnormality has occurred in the intermediate transfer belt 136 as the first transfer material on the condition that the determination unit 236 determines that the predetermined normal range is exceeded. An abnormality handling processing unit 260 that performs processing is provided.

  The abnormality handling processing unit 260 according to the present embodiment includes a storage unit 262 that stores a history of the occurrence of a characteristic abnormality in the intermediate transfer body belt 136 that is the first transfer material, and a characteristic abnormality in the intermediate transfer body belt 136. A notification unit 264 that notifies the user, the management center, and the like of the information that the occurrence of the error occurs, and a stop control unit 266 that stops the image forming process.

  Although the current value detected by the output current detection unit 234 can always be stored in the storage unit 262, in this case, the amount of information becomes enormous. In order to reduce the storage capacity of the storage unit 262, it is preferable to leave only the minimum necessary information. Here, for practical purposes, it may be considered sufficient that an abnormality occurs to be left as the current history.

  Therefore, the abnormality handling processing unit 260 responds to the occurrence of a characteristic abnormality in the secondary bias transfer roll 138 on condition that the determination unit 236 determines that the predetermined normal range (threshold value Th1) is exceeded. A process of leaving the current value detected by the output current detection unit 234 in the storage unit 262 is performed.

  FIG. 3 is a diagram illustrating an example of a current monitor value detected by the output current detection unit 234. The current monitor value pulsates due to unevenness of the intermediate transfer belt 136 or the like.

  The output current detection unit 234 is configured to measure a current value between the backup roll 137c and the secondary bias transfer roll 138. Specifically, in the state where a predetermined voltage (high voltage for transfer) is output to the secondary bias transfer roll 138 by the transfer high voltage power supply 222 and the voltage control unit 232, the intermediate transfer body belt 136 is rotated in the belt rotation direction. The output current value is detected and calculated at a plurality of positions in the cycle at a predetermined sampling cycle, and the current monitor value as shown in FIG. The transfer output voltage determination unit 238 is notified at a predetermined timing.

  The determination unit 236 determines that a characteristic abnormality has occurred in the secondary bias transfer roll 138 when the current monitor value at each sample point sampled by the output current detection unit 234 deviates from the predetermined normal range. to decide.

  Here, as shown in FIG. 3, the current monitor value pulsates, and the average value is influenced by the setting by the transfer output voltage determination unit 238. Therefore, based on the magnitude of the current monitor value at each sample point itself. Rather than judging, it is better to use the degree of change as a judgment criterion.

  For example, when the difference Δ1 between the current monitor values at the respective sample points sampled by the output current detection unit 234 exceeds the preset threshold Th1, the determination unit 236 causes a characteristic abnormality in the secondary bias transfer roll 138. Is determined to have occurred.

That is, as the abnormality determination logic in the determination unit 236, as shown in FIG.
Difference between current monitor value (n) and current monitor value (n + 1)> threshold Th1: Abnormal Difference between current monitor value (n) and current monitor value (n + 1) ≦ threshold Th1: normal.

  Note that the determination unit 236, when the difference Δ2 between the maximum value MAX and the minimum value MIN of the current monitor value at each sample point sampled by the output current detection unit 234 exceeds a preset threshold Th2, It may be determined that a characteristic abnormality has occurred in the secondary bias transfer roll 138.

  When the determination unit 236 detects a characteristic abnormality of the secondary bias transfer roll 138, the abnormality handling processing unit 260 performs control according to the setting at the time of abnormality detection. It is preferable that the user can select and decide what kind of control is performed. Further, it is more preferable that a plurality of controls can be arbitrarily combined and selected and determined.

  For example, as the setting example 1, the abnormality handling processing unit 260 uses the history that the characteristic abnormality of the secondary bias transfer roll 138 is detected as a history, job execution date and time, job type (print, copy, etc.), job file Job information such as a name (print file) is stored in the storage unit 262 in association with identifiable information.

  The history of the occurrence of the characteristic abnormality in the intermediate transfer belt 136 stored in the storage unit 262 includes not only the abnormality in the intermediate transfer belt 136 but also the output current detection in the sense that the evidence remains. It is preferable to store information of each output current value at a plurality of positions in the circumferential direction of the intermediate transfer belt 136 detected by the unit 234.

  In this way, it is recognized that a characteristic abnormality has occurred in a part of the intermediate transfer belt 136 when the difference between measured values measured at a plurality of points exceeds a threshold Th1 that is arbitrarily set. The history can be accurately stored in the storage unit 262 inside the machine.

  For example, it becomes possible to determine later whether the cause of the failure is due to a user's operation error or the like, or a failure of the machine (in particular, the intermediate transfer belt 136 in this example). If an abnormality in the characteristics of the intermediate transfer belt 136 is detected and the history is left in the machine, it is specified what month and day the job has been processed, and the characteristics of the intermediate transfer belt 136 when an image defective print occurs. After confirming whether the abnormality has been detected, the cause of the malfunction caused by the intermediate transfer belt 136 can be explained to the user.

  Further, as setting example 2, when the abnormality handling processing unit 260 detects a characteristic abnormality of the secondary bias transfer roll 138, the abnormality handling unit 260 transmits the abnormality information of the intermediate transfer belt 136 to the display device, the audio device, or the like via the notification unit 264. The user is notified through a user interface using the multimedia device, and a processing instruction is awaited. The user instructs the re-output by changing the operation condition as necessary by the notification via the notification unit 264.

  When the characteristic abnormality of the intermediate transfer belt 136 is detected and the user is notified that the characteristic abnormality has occurred, the user can be inquired whether to execute the characteristic transfer as it is. Re-output after changing the operating conditions and re-output after failure repair can be executed, so image quality defects can be avoided.

  Further, as setting example 3, when the stop control unit 266 of the abnormality handling processing unit 260 detects a characteristic abnormality of the secondary bias transfer roll 138, the stop processing unit 266 stops the image forming process (printing process) as a failure state (Fail). As described above, the control signal CN4 is sent to the printing operation mechanism unit 340 for control. In this way, defective printing can be prevented by stopping printing when a characteristic abnormality of the secondary bias transfer roll 138 is detected.

  In this setting example 3, in combination with the setting example 2 described above, when an abnormality in the characteristics of the secondary bias transfer roll 138 is detected, the setting example 3 notifies the user via the notification unit 264 and also via the stop control unit 266. It is effective to stop printing.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above embodiment, a plurality of engines corresponding to each output color are arranged in-line, and a color image is formed by processing images of each output color in parallel (simultaneously) with each engine. The example applied to the tandem type color image forming apparatus configured as described above has been described. However, as long as the intermediate transfer type is provided with the intermediate transfer belt, the operation and effect of the print control unit 220 described in the above embodiment is achieved. The application range is not limited to the configuration of the above embodiment.

  For example, an image of each color is sequentially formed on an image carrier such as a photosensitive drum by a single engine (photosensitive unit), and this is overlaid and transferred to an intermediate transfer member (primary transfer material) one color at a time. The present invention can also be applied to a multi-pass type (cycle type) color image forming apparatus that forms a color image.

1 is a diagram illustrating a configuration example when an image forming apparatus according to the present invention is applied to a printer. FIG. 3 is a functional block diagram of a configuration example focusing on image forming processing in a second transfer unit of the printer illustrated in FIG. 1. It is a figure which shows an example of the current monitor value detected by the output current detection part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printer, 100 ... Printer main body, 102 ... Main unit, 103 ... Scanning output system, 105 ... Cartridge part, 107 ... Standard conveyance system, 108 ... Roll member, 130 ... Print execution part, 131 ... Photoconductor drum, 132 ... Cleaner, 133 ... primary charger, 134 ... developing device, 135 ... primary bias transfer roll, 136 ... intermediate transfer belt, 137c ... backup roll, 138 ... secondary bias transfer roll, 139 ... fixing unit, 139a ... fixing Roll, 139b ... Fixing discharge roll, 140 ... Belt cleaning unit, 179 ... Writing scanning optical system, 180 ... Manual tray, 182 ... MOB & ADC sensor, 184 ... Home position sensor, 186 ... Edge sensor, 190 ... Feed tray ... second transfer unit, 220 ... print control unit, 222 ... transfer high power Power source 230 ... Transfer bias control unit 232 ... Voltage control unit 234 ... Output current detection unit 236 ... Determination unit 238 ... Transfer output voltage determination unit 260 ... Abnormality response processing unit 262 ... Storage unit 264 ... Notification , 266 ... Stop control unit, 340 ... Print operation mechanism unit

Claims (11)

An image obtained by forming a latent image on the first image carrier and developing the latent image is transferred onto the first transfer material, and the first transfer material is transferred to the second image carrier. An image forming apparatus that forms an image on an output medium that is the second transfer material by transferring the image transferred onto the second image carrier onto a second transfer material,
A transfer unit that contacts and transfers the image formed on the second image carrier to the second transfer material;
A control unit that detects a transfer bias state in the transfer unit over a predetermined range corresponding to an image forming range on the second image carrier, and controls image forming conditions based on the detection result. An image forming apparatus. The image forming apparatus according to claim 1, wherein the control unit includes a transfer bias control unit that controls a transfer bias in the transfer unit. The first transfer material is composed of an endless belt,
The image forming apparatus according to claim 2, wherein the transfer bias control unit controls the transfer bias over a predetermined range of the first transfer material in a belt circumferential direction. The transfer bias controller
A voltage control unit for controlling a transfer output applied to the transfer unit;
An output current detector for detecting an output current value at the time of constant voltage control by the voltage controller;
3. A transfer output voltage determining unit that determines a transfer output voltage to the transfer unit controlled by the voltage control unit based on an output current value detected by the output current detecting unit. The image forming apparatus according to 3. The image forming apparatus according to claim 4, wherein the output current detection unit detects the output current value at a plurality of positions in one cycle of the first transfer material in a belt rotation direction. An image obtained by forming a latent image on the first image carrier and developing the latent image is transferred onto the first transfer material, and the first transfer material is transferred to the second image carrier. An image forming apparatus that forms an image on an output medium that is the second transfer material by transferring the image transferred onto the second image carrier onto a second transfer material,
A transfer unit that contacts and transfers the image formed on the second image carrier to the second transfer material;
A determination unit that detects a transfer bias state in the transfer unit over a predetermined range of the second image carrier, and determines whether the detection result exceeds a predetermined normal range;
An abnormality handling processing unit that performs processing in response to occurrence of a characteristic abnormality in the first transfer material on condition that the determination unit determines that the predetermined normal range is exceeded. An image forming apparatus. The image forming apparatus according to claim 6, wherein the abnormality handling processing unit includes a storage unit that stores a history that a characteristic abnormality has occurred in the first transfer material. The image forming apparatus according to claim 6, wherein the abnormality handling processing unit includes a notification unit that notifies information indicating that a characteristic abnormality has occurred in the first transfer material. The image forming apparatus according to claim 6, wherein the abnormality handling processing unit includes a stop control unit that stops the image forming process. An image obtained by forming a latent image on the first image carrier and developing the latent image is transferred onto the first transfer material, and the first transfer material is transferred to the second image carrier. As an image forming method for forming an image on an output medium that is the second transfer material by transferring the image transferred on the second image carrier to a second transfer material,
When the image formed on the second image carrier is contact-transferred to the second transfer material at the transfer unit, the image is formed over a predetermined range corresponding to the image forming range on the second image carrier. An image forming method comprising: detecting a transfer bias state in the transfer unit and controlling an image forming condition based on the detection result. An image obtained by forming a latent image on the first image carrier and developing the latent image is transferred onto the first transfer material, and the first transfer material is transferred to the second image carrier. As an image forming method for forming an image on an output medium that is the second transfer material by transferring the image transferred on the second image carrier to a second transfer material,
When the image formed on the second image carrier is contact-transferred to the second transfer material by the transfer unit, the transfer bias in the transfer unit over a predetermined range of the second image carrier. A state is detected, and it is determined whether or not the detection result exceeds a predetermined normal range. If the detection result exceeds the predetermined normal range, a characteristic abnormality has occurred in the first transfer material. An image forming method comprising performing an abnormality handling process.

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